These trucks are very sensitive when it comes to electronics. The first thing I would do is clean the TB inside and out if that doesnt do it, it could possibly be a bad ecu.

Here is a very good forum to list your problem Trailvoy.com - The Chevy Trailblazer and GMC Envoy Enthusiast Site theres a guy named Roadie he knows envoys and tb's like no tomorrow. PM him if you cant figure it out.